File Format Signaling of Error Mitigation in Sub-Picture Bitstream Based Viewport Dependent Video Coding

1. A method comprising: encoding pictures in sub-picture bitstreams in tracks by: ensuring no sample values outside a sub-picture are referenced for inter-prediction, restricting motion vectors to point to full-sample locations inside the sub-picture and to fractional-sample locations that employ only full-sample locations inside the sub-picture for interpolation, and restricting inter-prediction so motion vector candidates for temporal motion vector prediction are not derived from blocks outside the sub-picture; and encoding a track level mergable indication to indicate that a sub-picture bitstream carried in a current sub-picture track cannot be merged with a sub-picture bitstream carried in another track belonging to a same track group to generate a single video bitstream without decoding mismatches caused by rewriting only header data of the sub-picture bitstreams.

2. The method of claim 1 , wherein the track level mergable indication is included in a Sub-Picture Region Box.

3. The method of claim 1 , wherein the track level mergable indication, when set, further indicates that wavefront parallel processing is disabled.

4. The method of claim 1 , wherein the track level mergable indication is encoded in a track header box in a track box for each track containing one of the sub-picture bitstreams.

5. The method of claim 1 , wherein the track level mergable indication is encoded in a track group box describing associations between sub-picture tracks including the sub-picture bitstreams.

6. The method of claim 1 , wherein the track level mergable indication is encoded in a media box describing track media information.

7. A video coding device comprising: a processor configured to: encode pictures in sub-picture bitstreams in tracks by: ensuring no sample values outside a sub-picture are referenced for inter-prediction, restricting motion vectors to point to full-sample locations inside the sub-picture and to fractional-sample locations that employ only full-sample locations inside the sub-picture for interpolation, and restricting inter-prediction so motion vector candidates for temporal motion vector prediction are not derived from blocks outside the sub-picture; and encode a track level mergable indication to indicate that a sub-picture bitstream carried in a current sub-picture track cannot be merged with a sub-picture bitstream carried in another track belonging to a same track group to generate a single video bitstream without decoding mismatches caused by rewriting only header data of the sub-picture bitstreams.

8. The video coding device of claim 7 , wherein the track level mergable indication is included in a Sub-Picture Region Box.

9. The video coding device of claim 7 , wherein the track level mergable indication, when set, further indicates that wavefront parallel processing is disabled.

10. The video coding device of claim 7 , wherein the track level mergable indication is encoded in a track header box in a track box for each track containing one of the sub-picture bitstreams.

11. The video coding device of claim 7 , wherein the track level mergable indication is encoded in a track group box describing associations between sub-picture tracks including the sub-picture bitstreams.

12. A non-transitory computer readable medium comprising a computer program product for use by a video coding device, the computer program product comprising computer executable instructions stored on the non-transitory computer readable medium such that when executed by a processor cause the video coding device to: encode pictures in sub-picture bitstreams in tracks by: ensuring no sample values outside a sub-picture are referenced for inter-prediction, restricting motion vectors to point to full-sample locations inside the sub-picture and to fractional-sample locations that employ only full-sample locations inside the sub-picture for interpolation, and restricting inter-prediction so motion vector candidates for temporal motion vector prediction are not derived from blocks outside the sub-picture; and encode a track level mergable indication to indicate that a sub-picture bitstream carried in a current sub-picture track cannot be merged with a sub-picture bitstream carried in another track belonging to a same track group to generate a single video bitstream without decoding mismatches caused by rewriting only header data of the sub-picture bitstreams.

13. The non-transitory computer readable medium of claim 12 , wherein the track level mergable indication is included in a Sub-Picture Region Box.

14. The non-transitory computer readable medium of claim 12 , wherein the track level mergable indication, when set, further indicates that wavefront parallel processing is disabled.

15. The non-transitory computer readable medium of claim 12 , wherein the track level mergable indication is encoded in a track header box in a track box for each track containing one of the sub-picture bitstreams.

16. The non-transitory computer readable medium of claim 12 , wherein the track level mergable indication is encoded in a track group box describing associations between sub-picture tracks including the sub-picture bitstreams.